This invention relates to a machine tool spindle assembly, and more specifically, to a machine tool spindle assembly for firmly retaining a cutting tool therein at high spindle speeds notwithstanding machine tool vibration.
Machining of unfinished parts at ultra high speeds, that is, at speeds of 20,000 to 100,000 RPM, is often more advantageous than machining of such parts at low speeds (e.g. 200-3,000 RPM). Firstly, more material can be removed from an unfinished part during a given interval by machining at ultra high speeds than can be removed during the same interval by machining at low speeds. In addition, ultra high speed machining is more efficient because less horsepower is needed at such high speeds to drive the spindle than is required at low speeds. Further, ultra high machining results in a smoother surface on finished parts.
One of the major problems associated with ultra high speed machining has been retention of the cutting tool within the spindle. Machine tool vibration, usually of little or no consequence during low speed machining, can, at ultra high speeds, cause loosening of the cutting tool within the machine spindle. Loosening of the cutting tool within the spindle may not only result in damage to the cutting tool, but also damage to the unfinished part. More importantly, should the cutting tool become completely disengaged from the spindle during machining operations, serious injury to the machine tool operator can result if the machine cutting tool comes in contact with the operator.
Presently, there exists several different types of high speed machine tool spindles. One type of prior art high speed spindle includes a tool gripping collet integrated to one end of the spindle. The collet is urged radially inward against the shank of a cutting tool disposed within the spindle bore by a single collet nut in threaded engagement with the spindle adjacent to the collet. Another type of high speed machine tool spindle presently in use employs two or more set screws which are threaded into the spindle to bear against the flatted portion of the cutting tool shank. Most recently, a high speed machine tool spindle has been developed which has a bore tapered complementary to the taper of the cutting tool shank. A draw bar is carried within the spindle bore and threadedly engages the end of the cutting tool shank to draw the cutting tool into the spindle bore. Despite the differences among the above-described prior art high speed machine tool spindles, each is believed susceptible to machine tool vibration, which may likely cause disengagement of the cutting tool from the spindle.
It is an object of the present invention to provide a machine tool spindle which firmly retains a cutting tool therein at ultra high spindle speeds.
It is another object of the present invention to provide a machine tool spindle which firmly retains a cutting tool therein notwithstanding machine tool vibrations.